1. Field of the Invention
The invention relates to a control apparatus for an electromagnetically driven valve which is applied to an electromagnetically driven valve in which a movable portion including an armature and a valve element is driven using an electromagnetic force generated by an electromagnet, and which controls a mode of driving the movable portion, and a control method of the same.
2. Description of Related Art
As a conventional control apparatus for an electromagnetically driven valve of this type, for example, a control apparatus disclosed in Japanese Patent Laid-Open Publication No. 11-21091 has been known. This control apparatus realizes both operation stability and quietness of the electromagnetically driven valve by controlling a command current value, which is a command value for controlling a supply of current to an electromagnet, to be large when a movable portion is apart from a displacement end, and by controlling a command current value to be small when the movable portion is close to the displacement end.
Namely, the control apparatus controls an armature to be attracted to the electromagnet with reliability by making the command current value large in the case where the movable portion is apart from the displacement end so as to ensure the operation stability of the electromagnetically driven valve. Meanwhile, the control apparatus decreases a contacting speed and the like when the armature contacts the electromagnet by making the command current value small in the case where the movable portion comes close to the displacement end so as to suppress a contacting sound generated when the armature contacts the electromagnet, and ensure the quietness of the electromagnetically driven valve.
Also, the control apparatus performs feedback control for controlling a value of a current which is actually supplied to the electromagnet to be substantially equal to the command current value. Also, the control apparatus aims both to ensure responsiveness and to suppress hunting by controlling a feedback gain of the attracting current which is supplied to the electromagnet when displacing the movable portion to be larger than a feedback gain of a holding current which is supplied to the electromagnetic when holding the movable portion, when performing the feedback control.
The conventional control apparatus controls the value of the feedback gain of the attracting current and the value of the feedback gain of the holding current to be different from each other. However, each of the feedback gain of the attracting current and the feedback gain of the holding current is a fixed value. Therefore, the following trouble cannot be ignored which occurs since the feedback gain is fixed especially when the feedback of the attracting current is performed.
Namely, the responsiveness (the current responsiveness) depends on coil inductance of the electromagnet, that is, a distance between the electromagnet and the armature. Accordingly, when this feedback gain is controlled to be large so as to obtain excellent current responsiveness in a whole displacement area of the armature, hunting occurs in the attracting current in a certain displacement area of the armature. Meanwhile, when the feedback gain is controlled to be small so as to suppress such hunting in the whole displacement area of the armature, the current responsiveness deteriorates in a certain displacement area of the armature. Thus, it is difficult to perform appropriate feedback control of the attracting current in the whole displacement area of the armature, using the conventional apparatus.